This application claims the benefit of Japanese Applications Nos. 2000-120450 and 2000-153461 which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a defect testing apparatus for detecting a defect such as a foreign substance or a flaw on the surface of a substrate which may be produced in the course of manufacture of a semiconductor device, or the like, especially in the course of manufacture of a semiconductor wafer, a liquid crystal display panel, etc.
2. Related Background Art
In a conventional testing apparatus, a scattered light from the surface of a substrate to be tested is observed to detect an abnormality such as a foreign substance (e.g. dust) or a flaw. For instance, there is an apparatus which is disclosed in the Japanese Patent Laid-Open Application Nos. 5-232032 and 5-232040. According to the disclosed method therein, this apparatus is arranged such that a light from a light source is applied onto an object to be tested, such as a wafer, so as to visually detect the scattered light therefrom, thereby conducting a defect test.
Also, according to a method disclosed in the Japanese Patent Laid-Open Application Nos. 7-27709 and 8-75661, it is arranged that a light from the light source is applied onto a tested object such as a wafer, and the scattered light therefrom is fetched by a light receiving optical system to obtain a dark field image, thereby detecting a defect from this image by an image processing.
To be described more specifically, in the course of manufacturing a semiconductor wafer or a liquid crystal display substrate, presence of a foreign substance such as a dust is a hindrance to a processing for forming a correct circuit pattern, such as an etching or CVD (Chemical Vapor Deposition). Accordingly, it is generally conducted, on the stage of printing and developing a pattern on a resist typically by means of an exposure machine, to test to detect an abnormality or a foreign substance on the printed pattern. Such a conventional test of this type is conducted by applying a light flux from an illumination optical system onto an object to be tested to be visually observed by a testing personnel, as disclosed in the Japanese Patent Laid-Open Application No. 5-232032 described above. In this case, if the light is applied onto a fine circuit pattern in the course of detection of a foreign substance, a diffracted light is produced, which results in difficulty in discriminating the scattered light which is produced by the foreign substance from the diffracted light which is produced by the circuit pattern. Moreover, since a pattern abnormality is detected by using a diffracted light, a result of the test is easily affected by the degree of skill or of fatigue of the testing personnel so that the test standard is unstable. Accordingly, in the above Japanese Patent Laid-Open Application No. 7-27709, such a method is disclosed in which the illumination is optimized in detecting a foreign substance and in detecting a pattern abnormality with application of the technology of an image processing so as to attain a test free from an individual difference of the testing personnel. In this case, in order to detect a foreign substance on the surface of a tested object, an illumination light from the light source is introduced into a light guide fiber to form a linear secondary light source. Then, a light from the linear secondary light source is transmitted through a condensing lens so that a light flux in the direction of the surface on which the illumination light is incident is collimated to be substantially parallel light fluxes. Thereafter, the light is applied onto the entire surface of the wafer at an angle of incidence of substantially 90xc2x0. The scattered light from the foreign substance on the wafer is received by the light receiving optical system which is disposed above the wafer, whereby the foreign substance is detected.
However, in such a testing apparatus, if fine repeated patterns are present on the tested object, the diffracted light may enter the eye of the observer or the light receiving optical system to be hindrance to detection of a defect under a certain condition, which leaves the possibility that an abnormality such as a foreign substance of a flaw can not be detected.
Furthermore, the conventional apparatus described above is arranged such that in order to minimize an amount of light to enter the surface of the tested object so as to detect a scattered light from a foreign substance at a highest contrast, the illumination light illuminates the tested object at an angle of incidence of substantially 90xc2x0. For this reason, when the wavelength of the illumination light and the pattern pitch of the tested object are substantially equal to each other, the diffracted light advances in a direction substantially perpendicular to the surface of the tested object so as to enter the light receiving optical system. The amount of the diffracted light from the circuit pattern is far greater, compared with that of the scattered light from the foreign substance. For this reason, there arises a problem that the foreign substance can not be detected when the diffracted light is incident on the light receiving optical system of the surface testing apparatus. Particularly, in a case as disclosed in the Japanese Patent Laid-Open Application No. 7-27709, in which the illumination light is applied in the entire circumferential direction of the tested object, since the diffracted light inevitably enters the light receiving optical system, a test on a foreign substance can not be conducted.
The present invention was contrived taking such problems into consideration, and its object is to provide a testing apparatus and method with high reliability, which is arranged such that a diffracted light does not enter a light receiving optical system and capable of detecting a foreign substance, and the like, correctly at high speed and with high precision.
According to the present invention, there is provided a defect testing apparatus which comprises a light source, an illumination optical system for applying a light flux from the light source onto a substrate to be tested having repeated patterns at a predetermined angle of incidence, a light receiving optical system for receiving a scattered light from the tested substrate, an image pick-up device for picking up an image which is formed by the light receiving optical system, a display device for displaying the image obtained by the image pick-up device, and a test stage for mounting the tested substrate thereon at the time of testing, characterized in that the tested substrate and the illumination optical system are arranged to be rotatable relatively to each other.
The defect testing apparatus of the present invention may be arranged such that the test stage is rotatable around the axis in the normal direction of the tested substrate. Or, an alignment stage may be disposed separately to conduct alignment around the axis in the normal direction of the substrate prior to the test.
Moreover, the defect testing apparatus of the present invention preferably comprises a light receiving optical system which is telecentric on the side of the tested substrate.
Also, the defect testing apparatus of the present invention is preferably arranged, when a light is applied on the tested substrate with the spread angle on a flat surface which is perpendicular to the entrance surface of the illumination optical system and contains the optical axis, to rotate such that an angle of rotation between the optical axis of the illumination optical system and the direction of arrangement of lines of the repeated pattern is more than or equal to xc2xd of the spread angle.
Moreover, in the defect testing apparatus of the present invention, even when the repeated pattern has two or more directions of arrangement, the test stage or the alignment stage can be rotated to satisfy predetermined conditions.
Furthers the defect testing apparatus of the present invention may comprise light flux shaping member which makes the spread angle variable, or a calculation device for determining the spread angle and an angle of rotation of the tested substrate on the basis of pattern information of the tested substrate, or an image processing device for conducting an image processing to detect a defect on the basis of the information obtained by the image pick-up device. In this manner, it becomes possible to automatically conduct defect detection.
According to the present invention, the illumination optical system comprises not less than three groups of optical devices having a refracting power at least on a first plane containing the optical axis of the illumination optical system, and optical devices having a refracting power on a second plane which is perpendicular at least to the first plane and contains the optical axis. In this case, the term xe2x80x9cthe refracting powerxe2x80x9d contains the reciprocal of the focal length of a reflection system, in addition to the reciprocal of the focal length of a transmission (refraction) system, such as a lens or a refracting surface. In addition, the term xe2x80x9cthe optical devicesxe2x80x9d contains a transmission (refraction) optical device or a reflection type optical device.
In an actual circuit device or a liquid crystal display device, manufactured devices stand in line in an orderly manner so that directions in which diffracted lights are produced are limited. That is, if the tested object is rotated on the horizontal plane, the direction of the diffracted light is changed so that conditions for preventing the diffracted light from entering the light receiving optical system can be selected. According to the structure of the present invention described above, a range for the angle of incidence of the light flux for illuminating the tested object can be limited to a narrow one, so that it is possible to easily find the conditions which prevent a comparative alignment of the direction of incidence of the light flux for illuminating the surface of the tested object with the direction of repetition of patterns formed on the tested object, that is, the conditions for an azimuthal direction for preventing the diffracted light from entering the light receiving optical system.
It is also necessary to satisfy such conditions as preventing the diffracted light coming from the surface of the tested object from entering any part on the entire surface of the tested object, as described above, in order to convert images produced by a scattered light from the surface of the tested object into image signals collectively by means of an image pick-up device. To this end, according to the present invention, any point on the tested object is illuminated under the uniform illuminating conditions by employing a so-called telecentric illumination method in which light fluxes for illuminating respective points on the tested object are made to be substantially parallel to each other by means of the above-described arrangement.
As a preferable embodiment of the invention, the light receiving optical system preferably comprises an image pick-up device unit and preferably comprises a wavelength selection device for selecting a light with a specific wavelength on the illumination optical system side rather than the image pick-up device unit side.
If the wavelength of the illumination light is different, an angle of diffraction from a pattern is different. As a result, it is possible to prevent the diffracted light from entering the image pick-up device unit of the light receiving optical system by selecting or limiting the wavelength of the illumination light. In other words, even when a diffracted light enters the light receiving optical system with the specific wavelength of A nm, it is possible to prevent the diffracted light from entering the image pick-up device unit of the light receiving optical system with another wavelength of B nm. According to the present invention, in addition to the structure which allows a relative rotation between the tested substrate and the illumination optical system, there is provided a wavelength selection device so as to prevent a diffracted light from entering the image pick-up device unit more effectively. It is desirable to dispose a member for selecting the wavelength of a light to be received, such as a filter, between the light source unit for supplying the illumination light and the image pick-up device.